I am not sure that I understand the question. There is no issue at all with using your assigned ASN to different carriers and at different physical locations. This data is simply added to the routes that you advertise.
The issue that I think you are dealing with is what to do when you advertise the same network from two different physical locations. This generally means that your application infrastructure and your internal routing at the two locations need to know what to do with that particular application traffic.
The option that you mention is to have a direct internal connection between the two sites. This can be a metro ethernet as you mention. Or it could be some kind of internal tunneled connection over the internet that allows you pass the relevant traffic internally between the sites.
Other options might be available from your application owners based on the type of data being served and how that data or applications work. If this is some kind of read only public system and updates are rare or can be peridodic completely disconnected hosting is possible.